Doctors, nurses, parents, and other care providers all need to be able to rapidly and accurately measure a person's body temperature. To find out whether a person is sick, the first thing a care provider usually does is take the person's temperature. Someone running a fever is likely to have an infection. A doctor or nurse can tell a lot about how a patient is doing by monitoring the patient's temperature over time and noting how it has changed.
There are three kinds of thermometers in wide use today:
glass thermometers, PA1 "electronic" thermometers, and PA1 ear ("tympanic") thermometers. PA1 The measuring time is very rapid--usually less than two seconds. PA1 Because the ear is a dry orifice, cross-contamination is not much of an issue--and individual, disposable probe covers further reduce the already low cross-contamination risks. PA1 The theoretical accuracy of the measurement is very high (for example, on the order of one tenth of one degree). PA1 Because of the short measurement time and the use of the ear as the measuring point, it is possible to rapidly measure the temperature of children, invalids and sleeping patients--and in other situations where it is difficult to get a patient to sit still for thirty seconds with a probe under their tongue. PA1 is helpful to the nurse or other care provider in correctly, repeatably positioning the probe relative to the patient's eardrum, PA1 is inexpensive to make, PA1 is easy to place over the probe before use and easy to strip from the probe after use, PA1 is comfortable for the patient, and PA1 promotes measuring accuracy. PA1 Very easy to use. PA1 Easy to strip off probe after use. PA1 Much more comfortable to the patient. PA1 Unlikely to lodge in the ear canal. PA1 Foam provides a spring action to push itself out of the ear--helping to prevent it from becoming lodged in the ear. PA1 Will not cause scratches or other abrasive injury. PA1 Completely conformable, allowing a comfortable sealing of the ear canal. PA1 The patient can detect proper sealing by the effect it has on the change of hearing--allowing the patient to confirm to the nurse that the probe is properly in position. PA1 Prevents external light and heat sources from adding inaccuracies to the temperature measurement. PA1 Provides excellent thermal isolation between the ear canal and the thermometer probe body--improving measurement accuracy by reducing thermal drift associated with the cold junction of a thermal pile-type measurement instrument. PA1 Is an excellent thermal insulator and barrier. By limiting the amount of heat drawn off the ear canal, the ability to achieve repeatable measurements is greatly enhanced. PA1 Provides extremely low emissivity in the infrared wavelength band of interest--further reducing error factors introduced through reflection within the ear canal. PA1 Is inexpensive to manufacture. PA1 Stretches over the probe to retain the probe cover without any special retention tabs or other mechanisms. PA1 Can stretch to fit a variety of different configuration probes PA1 Provides conforming resiliency that accommodate a wide range of different ear sizes without being uncomfortable. PA1 Can, in one embodiment, provide an externally-bonded thin-walled pre-stretched barrier (which can be less than 0.0075 inches) of high-density polyethylene that is substantially transparent to infrared radiation of interest while providing an industry accepted form of infection resistance and control. PA1 Can be inexpensively vacuum-formed (or compression molded) from a sheet of closed-cell foam that is dye cut and further laminated with a sheet of high density polyethylene. PA1 Allows use of a variety of different oversized probe configurations. PA1 In one embodiment, preferred black or darker color foam provides greater repeatability by blocking extraneous light, absorbing stray ambient light, and having very low emissivity with negligible thermal mass.
Glass thermometers are very inexpensive, very small and easy to store, and don't require batteries or other special supplies. For this reason, glass thermometers are probably the most widely used temperature measuring device in the home. However, glass thermometers have the disadvantage that they are very slow in making measurements--they typically require several minutes to reach body temperature. This is uncomfortable for the patient, and may be very troublesome when it is necessary to take the temperature of a small child or an invalid. In addition, glass thermometers are typically accurate only to within a degree, may be susceptible to errors in placement, and can be broken easily.
Because of these disadvantages, most hospitals and doctors' offices now use instruments commonly known as "electronic" thermometers. Most of us have had our temperature taken by an electronic thermometer at one time or another. The electronic thermometer includes a portable, hand-held battery powered unit with a display, and a separate probe. A wire usually connects the probe to the hand-held unit. The probe is long and thin, and has the same general shape as a glass thermometer. To use this kind of electronic thermometer, a nurse first covers the probe with a long thin disposable plastic probe cover that completely covers the probe. The disposable probe cover helps prevent the spread of disease by avoiding direct contact between the reusable probe and the germs in the patient's mouth. The nurse then puts the end of the probe under the patient's tongue. An electronic temperature sensor within the probe electrically senses the patient's temperature, and sends a signal to a microcomputer in the hand-held unit. The hand-held unit usually beeps when the temperature measurement is finished, and displays the patient's temperature on the display. The nurse can then remove the probe from the patient's mouth, strip the probe cover off the probe, and throw away the used disposable probe cover.
This type of electronic thermometer has achieved wide acceptance in hospitals because it is reasonably accurate, can be used with familiar placement techniques, and is (because of its disposable, replaceable probe covers) easily reusable for a number of different patients. Although the electronic hand-held unit is itself more expensive than most households are willing to pay, the overall cost of using this kind of electronic thermometer is relatively low because the disposable probe covers are inexpensive (two to three cents per cover, for example) and a single hand-held electronic unit may last for years and can be used to take the temperatures of many thousands of patients.
Electronic thermometers offer speed, ease of reading, and accuracy improvements over glass thermometers, and also eliminate the possibility of mercury poisoning. Although such electronic thermometers have achieved a fair degree of success, they have certain significant disadvantages. For example, they need to be constantly calibrated, are relatively easily broken, and often require a relatively long time (thirty seconds or more in many cases) to make an accurate measurement. There are also problems with taking a temperature from the patient's mouth due to breathing, keeping the thermometer under the patient's tongue, etc. Cross-contamination of infectious diseases is also a concern because the mouth is a "wet orifice."
More recently, a new kind of electronic thermometer has appeared on the market. This new kind of thermometer works by measuring the temperature of your eardrum. Since the eardrum is also known as the "tympanic membrane," these thermometers are sometimes called "tympanic thermometers."
Why the eardrum? The carotid artery that supplies blood to the hypothalamus--the body's temperature control center--passes through the eardrum. For this reason, the temperature of your eardrum corresponds very closely to the core temperature of your body. Although doctors and scientists have known this fact for many years, only since the mid-1980's have commercial devices been available to measure eardrum temperature in a clinical setting.
Ear or "tympanic" thermometers work by receiving and analyzing the radiant heat ("infrared") energy coming from the eardrum. Just as you can feel the heat when you hold your hands up in front of a warm fire, a tympanic thermometer can detect eardrum temperature without having to actually touch the eardrum by receiving the radiant heat energy coming from the eardrum.
Commercially available tympanic thermometers consist of a portable, hand-held battery powered main unit providing electronics, a display and a probe containing a "thermopile" or pyroelectric heat sensor. This special heat sensor called a "thermopile" is especially sensitive to the eardrum's radiant heat energy. Microelectronics can determine eardrum temperature from the electrical signals provided by the "thermopile" sensor. The thermopile's sensing probe or "nacelle" is typically an integral part of the tympanic thermometer's main unit--reducing the potential for breakage of the sensor assembly and (at least potentially) increasing reliability and accuracy.
The sensing probe typically has a tapered or cone shape for easy insertion into the outer ear canal. All of the commercially available tympanic thermometers accept disposable probe covers. These disposable probe covers further minimize the risk of spreading disease, and also promote cleanliness by preventing ear wax and other secretions from contacting the probe. Different manufacturers have different probe cover configurations (see FIGS. 1A-1B), but all of these probe covers have the common characteristic that they are relatively transparent to (and thus do not block or reduce) the radiant heat energy given off by the eardrum.
To use the ear thermometer, a nurse or other care provider inserts a disposable probe cover onto the instrument's sensing probe. Once the disposable probe cover is in place, the nurse or other caregiver inserts the covered probe into the patient's outer ear and then presses a button to command the instrument to make a measurement. The measurement time is usually very rapid--on the order of two seconds or less. The patient's temperature instantly shows on the instrument's display. The instrument may then be removed from the patient's ear, and the disposable cover can be stripped off the instrument and discarded.
Ear thermometry has advantages over other temperature measuring techniques:
Despite these many clear advantages, ear thermometry has not yet achieved wide success in the medical marketplace. Even though many hospitals are believers in the concept of ear thermometry, the hospital market overall has converted less than twenty-five per cent of its temperature measurements to ear thermometry--and the hospitals that have converted are often displeased with their choice.
The main reason for past failures is that existing ear thermometer/probe cover combinations do not provide the high, repeatable accuracy required in a demanding hospital environment. Nurses are often unable to duplicate ear thermometer readings. If you try to measure the same person's temperature twice with existing commercial ear thermometer/probe cover combinations, you may get two very different readings. Since accurate, repeatable temperature measurements are important or even critical to medical diagnosis and treatment (for example, to detect a 101.5.degree. F. hospital fever threshold or to establish a temperature pattern over time), it is important for temperature measurements to be as accurate and repeatable as possible.
For an ear thermometer to make an accurate, repeatable measurement, the ear thermometer probe must be aimed directly at the eardrum. Readings will be different unless the orientation of the probe within the ear is duplicated nearly exactly from one reading to the next. Because different structures within the ear give off, absorb and reflect different amounts and types of radiant energy, even slight differences in alignment between the probe sensor and the patient's eardrum can cause significant differences in the temperature reading.
Poor technique is the leading cause of ear thermometer inaccuracy and non-repeatability--and disposable probe cover design is an important factor in the nurse's ability to repeatably, correctly align the probe within the patient's ear. There have been several general approaches to tympanic thermometer probe cover design in the past. In one design approach, the disposable probe cover has a generally rigid structure designed to guide and place the probe (see FIGS. 1A & 1B for examples). In another design approach, the probe cover has very little structure, acting solely as a barrier against contamination and playing no role at all in probe placement (see FIGS. 1C & 1D for examples).
FIGS. 1A-1D show some examples of prior art tympanic thermometer probe covers. Prior art FIGS. 1A and 1B show examples of prior art probe covers that are designed to assist in guiding and placing the probe. The FIG. 1A prior art probe cover 10 is made by Thermoscan, Inc. of San Diego Calif. and marked with "U.S. Pat. No. 5,088,834". This probe cover 10 is made out of a single unitary piece of thin, lightweight, semi-rigid, stiff hollow translucent plastic material shaped into a cone 12. The cone 12 includes a thicker "shank" portion 18, and terminates in a thinner end portion 13 comprising an integral piece of thin plastic film 14 that is impervious to moisture but transparent to (and does not absorb) radiant heat energy at the infrared wavelengths emitted by the eardrum. The FIG. 1A one-piece probe cover 10 is designed to be inserted over a correspondingly cone-shaped probe. A surrounding retaining ring base 16 retains cover 10 on the probe during use. When cover 10 is inserted over the probe, plastic film 14 is stretched tightly over the end of the probe to provide a thin, wrinkle-free film "window" that is substantially transparent to infrared radiant energy. The conically shaped stiff "shank" portion 18 of cover 10 tapers to glide into the passageway of a person's ear leading to the eardrum--thus helping to position the probe relative to the eardrum. This stiff construction also allows probe covers 10 to be stacked one inside another for compact shipment.
FIG. 1B shows a different prior art probe cover 20 sold by Sherwood Medical Co. of St. Louis, Mo. (this design is also explained in Sherwood's U.S. Pat. Nos. 5,516,010, 5,293,862, 5,179,936, 4,790,324, 4,662,360 and/or 4,602,642 and possibly also in a still-pending continuing application of these). The FIG. 1B probe cover 20 comprises a thick rigid plastic cone 22 for insertion into a person's ear. Probe cover 20 is made out of injection molded, rigid polyethylene or polypropylene white plastic. Small tabs or "ears" within the hollow inner space formed within plastic cone 22 retain cover 20 on a specially designed corresponding probe. Plastic cone 22 terminates in a circular opening 24. A retaining ring 26 formed around opening 24 retains a thin transparent polypropylene or polyethylene plastic film membrane 28. Film membrane 28 is in an unstretched and wrinkled condition when the cover is not in position over a probe. When rigid probe cover 20 is inserted over a probe, the film membrane 28 stretches over the probe end to remove the wrinkles and provide a thin, substantially transparent film layer of uniform thickness. This stretched film layer 28 allows infrared radiant energy to pass through and reach the infrared probe inside rigid probe cover 20 without letting fluid, earwax, germs or anything else from the ear cavity come into contact with the probe.
The rigidity of disposable probe covers 10, 20 shown in FIGS. 1A and 1B can help a nurse insert the probe into and position the probe within the patient's ear. The rigidity of these probe covers 10, 20 also facilitates easy ejection of the probe covers from the probe after measurement. Unfortunately, this same rigidity makes these probe covers exceedingly uncomfortable for the patient. Because every person's ear has a different opening size, the "one size fits all" approach of the FIG. 1B probe cover 20 leads to discomfort and other problems. For example, probe cover 20 shown in FIG. 1B is known to become stuck in a person's ear, and can also scratch the inside of the ear. Frequently also, the probe tip will puncture the membrane film of the FIG. 1B probe cover when the clinician is inserting the thermometer into the probe cover.
The FIG. 1A probe cover 10 design is somewhat less uncomfortable than the FIG. 1B design, but the rather large diameter of conical shank 18 can be uncomfortable for some people. Moreover, its unitary, one-piece construction requires sophisticated techniques for drawing thin film portion 14 from the relatively thicker shank portion 18 during manufacture without puncturing the film. Also due to their rigidity, the FIG. 1A and FIG. 1B designs do not allow for total sealing of the ear canal to prevent external light and heat from entering during a measurement--degrading the accuracy and repeatability of temperature measurement.
FIGS. 1C and 1D show example prior art probe covers that follow a different approach of being mechanically transparent so as not to affect probe placement in any way. The FIG. 1C probe cover 30 is manufactured by Diatek, Inc. of San Diego, Calif. See U.S. Pat. No. Re. 34,599. This probe cover 30 includes a flat paper backing 32 that supports a piece of transparent film 34. Film 34 is stretchable, and completely envelopes the probe when cover 30 is placed over the probe--stretching tightly over the probe so as to provide a radiation-transparent film layer between the probe and the patient's ear. The FIG. 1C design has several advantages, including inexpensive construction, flat storage, and stackability. A big disadvantage of the FIG. 1C probe cover 30 is that the probe cover is of no assistance in reliably, repeatably positioning the probe within the person's ear. This probe cover 30 is designed to be used with a temperature sensing "gun" also manufactured by Diatek (see U.S. Pat. No. 4,863,281)--an unpopular design because of the bad connotations associated with putting a gun to someone's head.
FIG. 1D represents another prior art probe cover 40 manufactured by Exergen Corp. of Newton, Mass. and marked "U.S. Pat. No. 4,993,419." This disposable probe cover 40 comprises a film sheet 42 that is dispensed in a pre-perforated roll. In use, the nurse inserts a pin portion of the ear thermometer positioned opposite the probe into a first hole 44, and then wraps film 42 around the front of the probe and continues wrapping until a second hold 46 is aligned with the same pin portion. The nurse can then tear sheet 42 from the rest of the roll along the line of perforations 48. Holes 44, 46 retain sheet 42 on the probe during measurement. Although probe cover 40 is inexpensive to manufacture, it is difficult for a nurse to position properly onto the probe. In addition, the FIG. 1D probe cover 40 may not always reliably wrap around the front portion of the probe--creating wrinkles that can effect measuring accuracy. The FIG. 1D probe cover 40 can also slip off the probe without the nurse realizing.
The FIG. 1D cover also has repeatability problems. In actual use, clinicians regard repeatability as implying accuracy. If the same reading can be obtained from the same ear, within several tenths of a degree, then the thermometer is regarded as accurate, regardless of the actual core temperature of the patient. All of the manufacturers currently recommend that if a second temperature measurement is required, that it should be made in the other ear. The reason for this is not obvious, but it does have a tremendous bearing on a major problem concerning accurate measurements.
Simply stated, because the nacelles of tympanic thermometers are generally at or near room temperature, which can be up to forty degrees below patient core temperature, the nacelle can rapidly draw off heat from the ear canal, impacting successive measurements dramatically. An excellent demonstration of this effect is to place the Exergen unit in a patient's ear and leave it in place for about a minute, while taking temperatures every ten seconds during this time frame. The average decrease in readings is always several degrees over a minute. The Exergen models produce the most dramatic thermal reductions because the heat transfer is taking place between the ear canal, a FIG. 1D thin layer of film, and a large stainless steel mass. To a lesser extent, the FIG. 1A-1C probe cover designs exhibit the same, effect, albeit to a lesser extent.
As evidenced by the example prior art tympanic thermometer probe covers shown in FIGS. 1A-1D, there is a long felt but unsolved need for an ear thermometer disposable probe cover that:
No prior solution meets all of these needs.
The present invention provides a new disposable probe cover for an ear thermometer that meets all of these needs and provides other advantages as well. The disposable probe cover provided by this invention is made from a compressible, deformable material such as plastic foam. The disposable probe cover provided by this invention has the following advantages: